1. Field of the Invention
The invention pertains to the field of synthesis gas production and recovery of hydrogen gas therefrom, especially wherein said synthesis gas is obtained from coal hydrogenation residues.
2. Background of the Invention
A method is disclosed in U.S. Pat. No. 3,075,912 according to which, residues from coal hydrogenation which are separated from the gaseous and liquid products of the hydrogenation in hot separator units, wherein phase separation occurs at the pressure and temperature of the reaction or at a slightly lower temperature, are used to produce synthesis gas from which hydrogen is recovered, e.g. to be used in the original hydrogenation process. In addition to solids (such as unreacted coal, ash, and catalysts) and non-volatile liquids or viscous intermediate products (such as asphaltenes and pre-asphaltenes), the hydrogenation residues contain valuable volatile product oils which must be separated out before the gasification in order to improve the yield of liquid product.
Various methods, such as filtration, centrifugation, vacuum distillation, etc. are known for removing these volatile oil components. The oils recovered may then be used as slurry oils or components of slurry oils for the coal material being hydrogenated. Some of the oil separated by filtration or centrifugation contains a substantial fraction of impurities in the form of non-volatile, difficultly hydrogenatable, oil-soluble intermediate products, e.g. asphaltenes and pre-asphaltenes, which are detrimental to the hydrogenation process and for which much more severe hydrogenation conditions are required in order to break them down.
The above difficulties may be overcome by employing vacuum distillation. The oils recovered by vacuum distillation of the hydrogenation residue are valuable as slurry oils, or may be further hydrogenated under relatively mild conditions. However, the vacuum distillation residues present major handling problems. In particular, such residues are very difficult to remove from the vacuum distillation column and to transfer to the gasification apparatus as well as to charge into the latter, because of the high viscosity of the materials which have a high proportion of solids.